Nature’s Calendar demonstrates the impact of climate change on nature

Natural processes such as the flowering of trees and the start of bird migration take place every year during a specific period of time.

This thus creates nature’s calendar. At, is a collection of observations of annually recurring biological phenomena. Using this data, it is possible to map out the impact of climate change on nature and the consequences of this.


Nature’s Calendar is an initiative of the Environmental Systems Analysis chair group at Wageningen University and the VARA radio programme Vroege Vogels (Early birds). It is an observation programme which involves observing, analysing, predicting and communicating annually recurring biological phenomena. This branch of science is called phenology. Examples of those annually recurring phenomena are the time of flowering, leaf development and the fall of leaves from plants, but also the start of bird migration and the appearance of butterflies and other insects.

Phenology does not necessarily have to be performed by scientists. Everyone can do this, if necessary in their own back gardens. Nature’s Calendar is put together with a great deal of help from observers; these are people from throughout the Netherlands who report that fruit trees are in flower, who have observed the first hedgehog or grass snake, or who have seen the first butterfly in flight. These observations will be reported through the Nature’s Calendar website.

Observation programme

Based on the observation programme, Nature’s Calendar will map out ecological changes. The main objectives of this are:

  • to increase the understanding of the impact of changes in the weather and climate on nature in the Netherlands;
  • to increase the involvement of people in nature in their immediate surroundings;
  • to map out the impact of biological changes on health, agriculture and the management of green space;
  • to aid society when adapting to biological changes;
  • the development of interactive ecological educational programmes for students and adults.

Biological changes

An example illustrating why it is important to map out the biological changes is the advance of the oak processionary caterpillar. This species has been found in the Netherlands since the early 1990s and has been advancing further still. The caterpillar has barbed hairs which endanger health. Information from Nature’s Calendar will be used to register when and where the caterpillar occurs and will inform and warn people about the creature. The information will, however, also be used to be able to adequately combat the caterpillar. This brings together a number of objectives of Nature’s Calendar.

Climate change

Nature’s Calendar has been in existence since 2001 and has many partners. The observations of 7,000 people about 227 species are reported through the website.
Phenological observations were also carried out in the Netherlands prior to the start of Nature’s Calendar. For example, data from 1868 was already available about the flowering of snowdrops. With observations from the past and data from Nature’s Calendar, it will be possible to sketch an increasingly improved picture of the impact of climate change on nature in the Netherlands. For example, in relation to health or agriculture. At the same time, investigations will be performed on how best to deal with this impact.